The invention relates to security and/or valuable documents comprising at least one scratch-resistant coating as the top layer on at least one outer side, a process for the production thereof, a thermoplastic film coated with such a scratch-resistant coating and a lacquer composition for such a scratch-resistant coating.
Security and/or valuable documents, in particular identification documents, such as e.g. personalized ID cards, are in general produced by laminating several different layers which assume various functions in the card, usually in the form of individual films, to form a card. Structures with dimensions in the μm range are often additionally impressed here into the outer surface as security features during the laminating operation.
However, the thermoplastic materials preferably employed for such documents as a rule have relatively soft, scratch-sensitive surfaces. As a result, the readability suffers during the life of such a document of up to ten years. Security features can moreover be destroyed.
A further typical requirement of personalized ID cards is flexibility and breaking strength. In spite of often repeated flexural stress, the functioning of the card itself, but also of incorporated components, such as electronic chips or RFID antennae, should not be impaired.
Card reading apparatuses specifically often lead to scratches on the card surface, which reduce the flexibility and breaking strength of the card and therefore shorten the life of the card.
In order to ensure the functionality of the cards over their life mechanically and also with respect to readability, many manufacturers of personalized ID cards attempt to provide the outer sides of the cards with a scratch-resistant protective layer, which furthermore should have a good resistance to chemicals.
Conventional scratch-resistant lacquers based on acrylates, such as are used for electronics housings and lenses/displays, have outstanding scratch resistances and resistances to chemicals due to their high crosslinking density. The disadvantage of such systems, however, lies in an embrittlement accompanying the crosslinking density. This has the effect that the breaking strength of the card is impaired overall due to notching (fracture in the coating).
A further disadvantage is that the impressability of such highly crosslinked polymers is reduced. The highly crosslinked polymer can no longer be deformed sufficiently to accommodate relatively fine structures of the master in an adequate image sharpness.
There are set-ups for introducing into the coating, for flexibilizing such highly crosslinked scratch-resistant coatings, non-crosslinked polymers, such as e.g. polyvinyl acetate (cf. JP-A 2009-028956) or polyethylene wax (cf. JP-A 2008-006708). In this case, however, the resistance of the coatings to chemicals and therefore the life of the documents are reduced.
Possibilities also exist for subsequently laminating scratch-resistant coatings, which, for example, do not withstand the high laminating temperatures during the production of the ID cards, on to the finished card blank at lower temperatures via transfer films and optionally the additional use of adhesive layers (cf. e.g. JP-A 2005-280288, JP-A 2008-006708 and WO-A 2000/050250) or for subsequently applying them to the finished card blank as a lacquer coating (cf. e.g. JP-A 2004-315546 and JP-A 2000-119553). However, these processes comprise at least one additional, cost-intensive process step for application of the scratch-resistant coating. There is furthermore the disadvantage that in the case where transfer films are not used at the same time as the lamination of the card, impressing into the surface may take place, and in the case of subsequent application of a lacquer layer, any impressed structures are not retained in the desired sharpness.
There accordingly continued to be a need for a possibility of producing security and/or valuable documents, in particular identification documents, such as e.g. ID cards, with an outer scratch-resistant coating which withstands the relatively high lamination temperatures during the production of the documents, renders possible embossing with structures in the micrometer scale and meets the requirements of flexural and breaking strength of such documents, without thereby significantly losing scratch resistance or resistance to chemicals.